1. Field of the Invention
The present invention relates to a storage and delivery system for a capacitive deionized water treatment device used to purify a fluid, and in particular, for storing and delivering filtered water without requiring an additional pump, and without any appreciable loss of water.
2. Description of Related Art
Water softeners remove unwanted minerals, principally calcium and magnesium, from a hard water supply (correcting “high mineral content”) by using one of several water conditioning or water treatment methods. Water purification may be implemented by a variety of techniques, such as, reverse osmosis (RO), ion exchange, or electrodialysis, to name few.
The predominant process for water softeners to remove “hardness” (dissolved calcium and magnesium) is through ion exchange. Conventional water-softening appliances intended for household use depend on an ion-exchange resin in which “hardness ions”—mainly Ca2+ and Mg2+—are exchanged for sodium ions. Ion exchange devices reduce the hardness by replacing calcium and magnesium (Ca2+ and Mg2+) with sodium or potassium ions (Na+ and K+). Ion exchange resins are organic polymers containing anionic functional groups to which the dications (Ca++) bind more strongly than monocations (Na+). Inorganic materials called zeolites also exhibit ion-exchange properties. These minerals are widely used, for example, in laundry detergents. Resins are also available to remove carbonate, bi-carbonate, and sulphate ions, which are absorbed, and hydroxide ions released from the resin.
Incoming hard water passes through a tank of containing high-capacity ion exchange resin beads supersaturated with sodium. The calcium and magnesium ions in the water attach to the resin beads, replacing the sodium, which is released into the water. The softened water is then distributed for use throughout the house.
Over time, the ion exchange resin beads become saturated with calcium and magnesium ions. The resin must then be re-charged by eluting the Ca2+ and Mg2+ ions using a solution of sodium chloride or sodium hydroxide depending on the type of resin used. For anionic resins, regeneration typically uses a solution of sodium hydroxide (lye) or potassium hydroxide. The waste or backwash water eluted from the ion exchange column containing the unwanted calcium and magnesium salts are typically discharged to the wastewater treatment system. Sodium ions reclaim their position on the resin beads, and the calcium and magnesium ions are released into the backwash water. The number of times the tank is recharged and the amount of wastewater generated depends on a number of factors, including the hardness of the water, the amount of water used, the size of the water softener, and the capacity of the resins to remove calcium and magnesium.
A capacitive deionization (CDI) technique, which solely depends on electricity for performing water treatment and also for maintaining the equipment, presents an environmentally advantageous approach of being chemical and pollution-free. The method of capacitive deionization (CDI) does not use salt in this process, making it an eco-friendly choice for water decontamination.
CDI electrochemically removes ions from salty water. A saltwater process stream flows between two electrodes held at a potential difference generally around 1.2-1.5 V. Ions in the solution are attracted to the oppositely charged electrodes. The ions are electrosorbed onto the electrodes, removing them from the process stream, and the deionization cycle continues until the electrodes are saturated with ions. Then, during the regeneration cycle, the two electrodes are discharged or the polarity of the electrodes is reversed. This releases the ions into a waste stream, which has a much higher salt concentration than the process stream. This method has a much quicker cycle than typical water softeners using ion exchange resin beads, and at a lower cost.
In capacitive deionization, ions with a negative charge (anions) are removed from the water and are stored in the positively polarized electrode. Likewise, ions with a positive charge (cations) are stored in the negatively polarized electrode.
The major market advantage that CDI currently has over competing technologies is its ability to remove a wide range of ionic contaminants with high recovery rates. CDI can remove nearly all ionic contaminants—sulphates, nitrates, iron, arsenic and fluorides, along with sodium, calcium and magnesium salts.
The operation of CDI includes a series of charging and discharging of a flow-through capacitor comprising a positive electrode and a negative electrode. At the charging of the capacitor, a static electrical field is created between the electrodes of the flow-through capacitor, which readily adsorbs ions from water flowing between electrodes.
Generally, a capacitive deionization (CDI) filtration system is intended to be used to remove undesired concentrations of contaminants from fluids, such as salts dissolved inside the fluids. The CDI system may be intended for multiple applications both in the industrial, commercial, and retail fields, and used for such applications as: seawater desalination; softening of particularly hard water; and the removal from water of various unwanted substances, such as salts (such as chlorides and sulfates), nitrates, nitrites, ammonia, heavy metals, organic substances, and/or micro-pollutants in general. Moreover, other applications include the capability to deionize fluids in industrial processes or for the concentration of polluting substances that are difficult to dispose of or advantageous to recover for reuse.
Many industrial processes, for example treating metal surfaces such as phosphor-degreasing, polishing, anodization, painting, chromatizing, etc., foresee the use of water in the various productive processes, together with solutions of acids such as phosphoric acid, sulfuric acid, hydrofluoric acid, nitric acid, chromic acid, or rather alkalis such as degreasing products, phosphates, etc. The depuration of the wastewater from the industrial processes is one important aspect of the entire productive cycle, involving ecological, economic, and legal aspects.
The CDI filtration system is suitable for purifying water from ionized particles that are present and susceptible to the presence of an electrical field, such as for example ions in solution, and in particular calcium and magnesium which are the ions most responsible for the hardness of water and formation of limestone. To treat the stream as the water passes between electrodes, a voltage potential is established between the electrodes. This voltage potential causes constituents in the water to be attracted to and at least temporarily retained on one of the electrodes while the comparatively purified water is allowed to exit the capacitor.
Despite its intrinsic advantages, the limited plant efficiency and throughput of CDI technology has hindered its development into an industrial process. One of the reasons that affect its suitability is the low water recovery ratio (with respect to other processes used for brackish water desalination, for example), where the water recovery ratio is defined as the ratio of the amount of treated water obtained to the total amount of input water.
For a given throughput of a plant/process or water softening process, the water recovery ratio and the power consumption per unit volume of water treated are important metrics for judging the effectiveness of a plant/process. The costs of pumping, as well as pre- and post-treatment of water, adds to the rising costs of surface water and makes maximizing the recovery ratio a priority.